The question of whether a patient can receive LASIK after previously undergoing Photorefractive Keratectomy (PRK) is common for those seeking further vision correction. Both PRK and LASIK are laser refractive surgeries that reshape the cornea, the clear front surface of the eye, to correct common vision problems like nearsightedness or astigmatism. The core difference lies in how the surgeon accesses the underlying corneal tissue; PRK removes the surface layer, which regrows, while LASIK creates a hinged flap that is lifted and then repositioned. While technically possible in some specific cases, receiving LASIK after PRK is not the standard enhancement procedure, and safety depends entirely on the remaining corneal structure.
Understanding the Standard Enhancement Path
A need for further correction after an initial procedure is known as an enhancement. When a patient requires an enhancement following a PRK procedure, the clinical preference is almost always to perform a second PRK, often called a PRK touch-up. This approach is favored because it is a simpler continuation of the original surgical method, involving re-treating the corneal surface with the excimer laser. The second PRK avoids introducing the corneal flap—a new variable—to an already healed and reshaped eye surface.
Introducing a corneal flap, the defining step of LASIK, can complicate the healing process and risk assessment after a previous PRK. Attempting to create a LASIK flap using a microkeratome over a cornea flattened by PRK is generally not recommended due to a higher risk of creating an incomplete flap, known as a buttonhole. While modern femtosecond laser technology may mitigate some risk, the overall clinical rationale still favors the less invasive surface ablation technique for an enhancement.
The Critical Factor: Residual Corneal Thickness
The amount of tissue left in the eye’s central layer, known as the residual stromal bed, is crucial for the safety of any laser enhancement procedure. This underlying tissue maintains the structural integrity of the cornea. A specialized test called pachymetry is used to precisely measure the thickness before any decision is made.
If the residual stromal bed is too thin, the eye risks developing corneal ectasia, which is a progressive bulging and steepening of the cornea. The U.S. Food and Drug Administration (FDA) recommends that the untouched stromal bed remaining after laser ablation must be at least 250 microns (µm). However, many surgeons prefer to leave a residual bed of 300 µm or more to provide an extra margin of safety.
The calculation for LASIK after PRK must account for the original PRK ablation, the thickness of the new LASIK flap, and the tissue removed in the second laser ablation. Since the first PRK already reduced the overall corneal thickness, the remaining tissue must be robust enough to allow for flap creation (typically 90 to 150 µm) plus the new treatment depth. If the total corneal thickness cannot safely accommodate both the flap creation and the additional laser treatment, the patient is disqualified from the LASIK procedure.
Surgical Alternatives When LASIK is Not Possible
When the cornea is deemed too thin for subsequent LASIK or a second PRK, the most common alternative is still a PRK enhancement. This is a predictable and safe method to fine-tune vision after the initial procedure without the risk of flap complications. This option avoids creating a flap and is preferred when only a small amount of correction is needed.
For patients with higher residual prescriptions or critically thin corneas, a non-corneal procedure is often the best alternative. Implantable Collamer Lenses (ICLs), a type of phakic intraocular lens (IOL), are excellent choices because they are positioned inside the eye, typically behind the iris. Since ICLs do not require further removal of corneal tissue, they entirely bypass the thickness constraint that disqualifies a patient from further laser surgery.
Another option, often considered for older patients developing presbyopia, is Refractive Lens Exchange (RLE). This procedure involves removing the eye’s natural lens and replacing it with an artificial lens, similar to cataract surgery, which can correct a wide range of refractive errors. While these surgical options offer permanent correction, simple solutions like prescription glasses or contact lenses remain a safe and effective way to achieve the desired visual clarity.